These studies are concerned with dynamic aspects of whole body protein metabolism in human subjects and the adaptive response of body protein metabolism to change in diet. The major approach used involves the administration of N15-labelled amino acids for estimation or rates of whole body protein synthesis and breakdown. Studies will involve an examination of various models for exploring whole body N turnover and the effects of changes in protein and energy intake as these dynamic aspects of human protein metabolism. BIBLIOGRAPHIC REFERENCES: Winterer, J.C., Steffee, W.P., Perera, W.D.A., Uauy, R., Scrimshaw, N.S., and Young, V.R. 1976. Whole body protein turnover in aging man. Exper. Gerontol. (in press). Young, V.R., Uauy, R., Winterer, J.C., and Scrimshaw, N.S. 1976. Protein metabolism and needs in elderly people. in: Nutrition, Longevity and Aging (ed. M. Rockstein) Academic Press, NY (in press).